A function that allows iterating over both stdout and stderr concurrently, in realtime, line by line
In case you need to get the output stream for both stdout and stderr at the same time, you can use the following function.
The function uses Queues to merge both Popen pipes into a single iterator.
Here we create the function read_popen_pipes():
from queue import Queue, Empty
from concurrent.futures import ThreadPoolExecutor
def enqueue_output(file, queue):
for line in iter(file.readline, ''):
queue.put(line)
file.close()
def read_popen_pipes(p):
with ThreadPoolExecutor(2) as pool:
q_stdout, q_stderr = Queue(), Queue()
pool.submit(enqueue_output, p.stdout, q_stdout)
pool.submit(enqueue_output, p.stderr, q_stderr)
while True:
if p.poll() is not None and q_stdout.empty() and q_stderr.empty():
break
out_line = err_line = ''
try:
out_line = q_stdout.get_nowait()
except Empty:
pass
try:
err_line = q_stderr.get_nowait()
except Empty:
pass
yield (out_line, err_line)
read_popen_pipes() in use:
import subprocess as sp
with sp.Popen(my_cmd, stdout=sp.PIPE, stderr=sp.PIPE, text=True) as p:
for out_line, err_line in read_popen_pipes(p):
# Do stuff with each line, e.g.:
print(out_line, end='')
print(err_line, end='')
return p.poll() # return status-code